CN87106914A

CN87106914A - Method and apparatus for extruding food

Info

Publication number: CN87106914A
Application number: CN87106914.8A
Authority: CN
Inventors: 沃纳·维德曼
Original assignee: Werner and Pfleiderer GmbH
Current assignee: Werner and Pfleiderer GmbH
Priority date: 1986-10-30
Filing date: 1987-10-13
Publication date: 1988-10-05
Also published as: ES2030024T5; JP2617492B2; EP0265601B1; ES2030024T3; DK570287A; JPS63129977A; DE3777071D1; DK570287D0; EP0265601B2; DE3636867A1; ATE72946T1; AU595745B2; DE3636867C2; CN1017587B; EP0265601A3; EP0265601A2; US4786514A; AU7865487A

Abstract

A kind of method of ertruding food product, wherein raw-food material and water are admitted to extruder and mix in the mixed zone, and mixture is heated and plastifies, and extrudes by nozzle then.For keeping the mass conservation of product, detect the driving power (N) of motor, the throughput of raw-food material (m), (N m) obtains specific energy (S), and controller changes water supply so that specific energy keeps constant according to the value that presets by this tittle by a calculation element.

Description

Method and apparatus for extruding food products

The present invention relates to a method and apparatus for extruding food products.

In this method and apparatus, a biopolymer, such as starch or protein, is pressure cooked and expanded into a foam structure within seconds, generally by the action of shear forces. The word "cook-in extrusion" is thus also used.

Such a method for extruding a food product consisting of a starch carrier and protein is known from DE-OS3341090, in which the metered supply of water is effected by means of a flow control device at the beginning of the feed channel of the extrusion device. In this case, however, the metered supply of water is accomplished only by adjusting the water cut rate.

It is known from US-PS3711296 to increase the natural water content of the raw material by a suitable water supply. By varying the rotational speed of the extruder screw, the pressure and temperature conditions can be adjusted, at which the plastification necessary for extrusion can take place. Furthermore, it is known from this published document to provide a steam blowing zone in the second half of the extruder or to have a steam discharge zone along the extruder. The purpose of the steam discharge is to exclude as completely as possible the water vapor generated during plasticization.

The basic problems of such cooking extrusion operations are: in addition to the large fluctuations in the water content of the biological material, the fat content and the cellulose content also fluctuate, as a result of which the quality of the product, such as hardness, density, water solubility and viscosity, colour, taste, varies, and during the start-up fluctuations in the proportions of the individual components and fluctuations in the temperature of the material cause the same negative effects.

Starting from this, the object of the invention is to specify a method and an apparatus with which as many of these effects as possible occur are compensated for, so that a quality-invariant product is produced.

The present invention is based on the recognition that all end quality coefficients depend critically on the specific energy of mechanical input energy to Mass (Mass), on the retention time within the extruder, and on the temperature profile along the extruder product, due to the physical and chemical changes of the biopolymer caused by shear and heat transfer during the cooking extrusion operation. The required constant hold time profile means that the rotational speed of the screw and the mass flow of the biopolymer remain constant and the pressure conditions before the extrusion nozzle remain as constant as possible.

The mechanical input specific energy can be defined as the quotient of the net driving power and the total mass flow. The control of the input specific energy by means of the rotational speed is known from the rubber and plastic sector in order in this way to obtain a constant drift mass. Furthermore, it plays a role here by giving a certain temperature to the cabinet to influence the temperature. Due to the constant holding time required during the cooking press-as explained, it is not possible to keep the input specific energy constant by the rotational speed, and the holding time at high temperature during cooking is so short that there is only an auxiliary effect on the temperature of the cabinet.

According to the invention, these problems are solved by a method according to claim 1. The essence of the method is that the input specific energy is detected during the cooking extrusion operation and kept constant by varying the dosing water supply to the mixing zone and achieving a controlled injection of steam.

As a result, fluctuations in the moisture content of the product are completely compensated, and fluctuations in the fat content, sugar content or cellulose content of the product and fluctuations in the ratio are also appropriately compensated. At the end, the most decisive in accordance with the invention is the concept of keeping the input specific energy constant by the product humidity in the extruder. Control can be made between a water content of 0 to 50%. Keeping the input specific energy constant is most simply achieved according to claim 2 by adjusting the water supply in such a way that the temperature of the product in the extruder is not significantly affected. This effect on the temperature can be produced by the likewise possible supply or removal of steam.

Constant quality of the product is achieved by a superposition control according to claim 3, which compensates for a substantial part of all the generated fluctuations.

The supply and discharge of steam is preferably effected according to claim 4.

As a result of this superimposed control with the discharge and feed of steam at the appropriate location of the extruder, it is ensured that the temperature profile of the product is constant, in particular at the point of highest temperature, that is to say generally before the extrusion nozzle. The last three seconds in the cooking zone decisively determines whether heat exchange takes place and damage to the extrudate is caused. The control provided is preferably effected between 50mbar and 20 bar.

The moisture content of the product in the extruder is changed due to disturbances in the control of energy and temperature, thus changing the pressure loss of the extruder nozzle by viscosity. In many cases, this can lead to impermissible changes in the pressure return and the hold time profile, for which purpose the control is carried out by means of a mechanical product throttle in order to keep these parameters constant.

In order to enhance the control according to the invention and to obtain a desired temperature profile along the extruder, a controlled temperature can be imparted on a part of the housing wall according to claim 6.

Claims 7 to 12 relate to apparatus for carrying out the process, claim 7 relates to an arrangement with closed-loop control of the controlled water supply, claim 9 relates to control with controllable steam discharge or controllable steam supply, and claim 10 relates to control of the pressure in the extrusion nozzle.

Further details are given in the dependent claims.

The three closed-loop controls are preferably superimposed on one another and coordinated by a common computing device. In this case, the control by the water supply is of greatest importance due to the mechanical and exponential thermal influence on the product. In essence, the control influence by the supply and discharge of steam is small, due to the purely exponential heat influence. The least impact and therefore perhaps not desirable for many practical applications is the control of variable restriction through the extrusion nozzle nose, since there is only a linear thermal impact on the product.

Further features, advantages and details of the invention will appear from the following description of preferred embodiments with reference to the drawings. The figure is a schematic diagram, similar to a circuit diagram, of a cooking and extrusion apparatus with a measuring circuit and closed-loop control according to the invention.

In the drawing, an extruder 1 is shown, which comprises, in the direction of conveyance (arrow 2), in order, a mixing zone 3, a plasticizing zone 4 with a return flow 5, a cooking zone 6 and an extrusion zone 7 followed by an extrusion nozzle 8.

The screw 9 of the twin-screw extruder 1 is driven by a motor 10. The power consumption N of the motor 10 is detected by a power detection device 11 and sent to a central computing device 12. At the beginning of the extruder 1,

food preparation devices

13, 14 are provided, which

preparation devices

13, 14 feed the food material, for example, in a quantity of m_ZSugar and throughput of m_BIs fed into the extruder via

inlets

15, 16. In addition, the throughput is m_WIs also fed into the extruder. Quantity m_Z、m_BAnd m_WIs inputted to the center calculating means 12, the center calculating means 12 calculates from these quantities and the specific driving power S = (N)/(m) together_Z+m_B+m_W) Determining specific energy input (m) relative to the throughput of food_B、m_ZAnd m_WThe dimension of (d) is mass/unit time).

The central calculation means 12 outputs the actual value of the specific energy S thus found, which value is compared at a comparison point 17 with a desired value preset at the comparison point 17, the difference being a controlled condition at the input of the controller 18. The output of the controller 18 is connected to a rotational speed adjustment device of a water dosing pump 20At 19, a water metering pump 20 meters out the water entering the extruder 1 through an inlet 21. In this way, a first closed-loop control is formed, which is based on a preset desired value S_sollThe specific energy of the material to be mixed fed into the extruder 1 is maintained, wherein the water supply to be metered is varied and thus the viscosity of the material in the extruder is varied.

The second closed loop control is formed by a temperature sensor arrangement 22, the temperature sensor arrangement 22 being arranged in the region in front of the throttle valve 37 and detecting the temperature T_IstIs fed to a comparison point 23, where it is compared with a preset desired temperature value T at the comparison point 23_sollThe comparison is made and the difference is fed to an input of the controller 24. By means of the output of the controller 24, the regulating

devices

25 and 26 of the

steam throttle valves

27 and 28, respectively, are adjusted, by means of which steam

throttle valves

27 and 28 either high-temperature steam is injected before the plastification zone 4 via the inlet line 29 and the inlet 30 or steam is withdrawn after the plastification zone via the line 31 and the outlet 32 in order in this way to keep the temperature of the food product being processed constant.

The third closed loop control is formed by a pressure sensor 33, which pressure sensor 33 is arranged in the region in front of the throttle 37 and with which the actual pressure value P is detected_IstThis value is compared with the desired pressure value P at the comparison point 34_sollAnd (6) comparing. The difference is used as a controlled condition at the input of the controller 35 and the output of the controller 35 is connected to an adjustment device 36 for a throttle valve 37, the throttle valve 37 being positioned in front of the extrusion nozzle 8, the angle of which is adjustable and is only indicated approximately by a dashed line. The pressure condition changes according to the change in the angular position of the throttle valve 37.

The

controllers

18, 24 and 35 or the comparison points 17, 23, 34 are connected to the central computing device 12 (not shown in detail) and are controlled in a coordinated manner by the central computing device.

The compensation of the disturbance by three closed-loop controls will be described below.

In the region of the plasticizing zone 4 and the cooking zone 6,

devices

38 and 39 can be attached to give a certain temperature to the machine housing, which are shown schematically. By means of these means, a desired temperature profile can be preset, which is controlled by a controller, not shown in detail.

The above-described apparatus can be used for the production of various different food products using the method according to the invention. For example: breakfast cereals, snacks, corn chips, dried small bread, corn flour, physically and chemically treated starch, degerming spice, fruit wine gum and licorice sticks, livestock food, casein reactant to casein hydrochloric acid and alkalized substance of cocoa powder, etc.

Granular corn snacks will be used as a specific example of an application.

For this purpose, a twin-screw extruder ZSK70 was used, rotating in the same direction, with a screw diameter of 70mm and a rotational speed of 200 revolutions per minute. The throughput of the corn meal was 200kg/h and the water supply was 12 kg/h. The power consumption of the extruder was 8.5 Kw. The temperature given to the enclosure was controlled at 140 ℃. The input specific energy is fixed at 480 KJ/kg. The pressure in front of the mechanical product throttle was 73bar and the temperature in front of the extrusion nozzle was 170 ℃.

Starting from these basic conditions, the use of the device and the method according to the invention is explained below with the generation of various disturbances.

Example 1:

after more than 8000 hours of operation, the wear of the screw causes a reduction of 2mm in the diameter of the outer screw. As a result, the input specific energy rose to 500KJ/kg, the pressure rose to 93bar and the product temperature rose to 170 ℃. According to the invention, in order to compensate for this, the correcting variable "feed water" is increased by 2.5 litres per hour and the correcting variable "limit position" of the mechanical product throttle is reduced from an opening angle of 30 ° to 15 °.

Example 2:

fluctuations were produced in the feed in the form of an increase in the moisture content of the feed of 2.5% corresponding to 5 liters per hour. In this case, the input specific energy was reduced to 418KJ/kg, the pressure was reduced to 55bar and the temperature was reduced to 161 ℃. To compensate, the correcting variable "water supply" is reduced by 5 litres/hour.

Example 3:

the fat content in the raw material is increased by 2%. As a result, the input specific energy was reduced to 465KJ/kg, the pressure was increased to 77bar, and the temperature was reduced to 168 ℃. According to the invention, the correcting variable "steam venting" is corrected by increasing it, for example from 20% to 36% of the open throughput and the opening angle of the mechanical product throttle from 30 ° to 53 °. For the acceleration compensation, the energy control is carried out only temporarily. After this, the supply water is returned to the original value.

Example 4:

the three quantities mentioned above are generated superimposed on one another. According to the invention, compensation is effected by means of a superimposed control, the three correcting variables being changed simultaneously, the water supply being reduced by 2.5 litres/hour, the steam discharge being increased from 20% to 36% of the open throughput, and the mechanical product throttle being enlarged from 30 ° to 38 °.

Claims

1. A method of extruding a food product, in which food material and water are fed to an extruder and mixed in a mixing zone, the mixture is heated, plasticized by shear energy and foamed after passing through a nozzle, characterized in that the drive power (N) transmitted by a drive motor to a shaft or shafts is measured,

the volumetric throughput (m) of the product feedstock fed is measured, the quotient (S) of these quantities (N, m) is determined in a computing device, the specific energy (S) thus determined is fed as a controlled condition to a controller, which is operated in accordance with a preset desired value (S)_soll) In this wayThis way the specific energy is kept constant, i.e. the water fed to the mixing zone of the extruder and/or the steam fed as a correcting variable is controlled by the controller.

2. A method according to claim 1, characterized in that the water supply is adjusted by changing the rotational speed of a water dosing pump.

3. The method according to claim 1 or 2, characterized in that a control whereby the discharge of steam or the temperature of the added product of steam is controlled as a controlled condition by suitable adjustment is superimposed on a control whereby the input specific energy is kept constant by adjusting the supply water.

4. A method according to claim 3, characterized in that the controlled discharge of steam is performed in a zone after the plasticizing zone and the controlled injection of steam is performed in a zone before the plasticizing zone.

5. A method according to one of claims 1 to 4, characterized in that the pressure in front of a mechanical product restriction arranged in front of an extruder nozzle of the extruder is measured and kept constant by adjusting the product restriction.

6. Method according to one of claims 1 to 5, characterized in that the extruder housing part is given a temperature through the housing shell.

7. An apparatus for carrying out the process according to one of claims 1 to 6, comprising an extruder, feed means for feeding product material and water into the mixing zone of the extruder, an electrically controlled drive motor for the shafts or shafts of the extruder, characterized in that it comprises a device for determining the power consumption of the drive motor, a device for determining the throughput of product material, a device for regulating the various metering of water and/or steam, a computing device which is connected to the device for determining the throughput of product material and to the device for determining the power consumption and which is connected to a controller, the output of which is connected to the regulating device for water and/or steam supply, the water and steam supply being metered.

8. Apparatus according to claim 7, characterized in that the means for adjusting the water supply which can be dosed is a dosing pump.

9. An apparatus for carrying out the method according to one of claims 1 to 6, comprising an extruder, feed means for feeding the product raw material and water into the mixing zone of the extruder, an electrically controlled drive motor for the extruder shaft or shafts, characterized in that the extruder has a measuring device in the area before the extruder nozzle for measuring the temperature of the product, and a steam discharge line with a steam throttle valve in the area after the plasticizing zone, the temperature measuring device being connected to the input of a controller, the output of which is connected to the steam throttle valve.

10. The apparatus as claimed in claim 9, characterized in that in the region before the plasticizing zone there is a steam injection line with a steam throttle valve, which is connected to the output of the control, which is downstream of the temperature measuring device.

11. Apparatus according to one of claims 7 to 10, characterized in that a pressure detection device is arranged before the mechanical product restriction, which pressure detection device is connected to the input of the controller before the extrusion nozzle, the output of the controller being connected to the servomotor of the mechanical product restriction.

12. Device according to one of the claims 7 to 11, characterized in that the controller is connected to the computing means.